Cathode ray filter



ocrn 22, 1957 A K. F. Ross 1 2,810,859

zATHoDE RAY FILTER Filed May 2,7. 1955 United States Patent My presentinvention relates. to a cathode ray iilter for electromagnetic waves.This application is a continuation-in-part of my co-pending applicationSer. No. 155,205, led April 1,1, 1950, now Patent No. 2,728,854, issuedDecember 27, 1955.

An object of my present invention is to provide means in a cathode rayVtube for `discriminating between waves of different frequencies andselectively producing an output representative of one or more ofsuchwaves.

Another objectof this invention is to provide a lter adapted to acceptcertain wavelengths within a given band while rejecting otherwavelengths, in combination with means f-orinterchanging the pass andstop bands r.of such iilter.

A further object of the invention is to provide sharply discriminating`filter `means for channeling single-frequency waves of differentamplitudes into respective signaling circuits. p

In a system as herein disclosed there are provided rst and seconddellecting means for deflecting the beam of ,a cathode ray tube indifferent (usually perpendicular) planes, in combination with a networkfor varying the relative phase of signal waves applied to these twodeflecting means in dependence upon their frequency. (A similar systemutilizing a network forvarying the relative amplitude, rather thanphase, of such signal wavesl has been disclosed and claimed inco-pending application Ser. No. 155,207, led April 11, 1950 by PhilCutler and myself, now Patent No. 2,728,911, issued December 27, 1955.)

A feature of the instant invention resides in providing,

in a cathode ray tube system as set forth above, a plurality ofconcentric annular output electrodes each shaped and positionedtoregister with the trace of the beam when the latter is deflected by asignal of predetermined frequency and amplitude; if these outputelectrodes are all similar to each other (e. g. all'circular), they will50 all respond to signals of the same frequency but of differentamplitudes.

Another feature of my invention resides in the provision of an outputelectrode having at least one but not more than two axes of symmetry,each axis of symmetry being inclined with respect to the two planes ofdeection of the beam. .An electrode of this description has a preferreddimension which, if positioned at a 45 angle relative to the planes ofdeflection, will coincide with the axis of an ellipse which will be themajor axis for some frequencies and the minor axis for others. Arelatively large output will then be obtainable from waves in thefirst-mentioned frequency group while only a negligible output willresult from waves of said other ,frequencies. When the connectionsbetween the signal source and the two deecting means are reversed, thepositions of the two frequency groups in the spectrum are interchanged.

Advantageously, therefore, a cathode ray tube accordi ing to theinvention comprises target means in the shape of a plurality ofdistinctly elliptical, concentric and similar ellipses whose major andminor axes extend at 45 angles with respect to two perpendicular planes,in combination with means for subjecting the beam of the tube toout-of-phase deiiectingforces in said two planes derived from thesamerinput signal. Y

, My invention will be more fully described with reference to theaccompanying drawing in which:

Fig. 1 shows acircuit arrangement of a cathode ray tube system embodyingthe invention; and

Figs. 2-7 illustrate` different targets adapted to be used as outputelectrodes with the system of Fig. 1.

Throughout the drawing, similar elements have been denoted by the samereference numerals prefixed by different hundreds digits identifying therespective ligures.

In Fig. 1 there is shown a cathode ray tube 100 cornprising a source ofelectrons shown as a cathode 101 and focusing or beam-forming meansshown as a first anode 102 and a second or accelerating anode 103. Theelectrodes 101, 102 andiV 103 derive their potentials from a battery 104and a potentiometer 105 in series therewith,

Two pairs of deiiecting electrodes 106', 106" and I107',

107", arranged in mutually perpendicular planes, receive signals frominput terminals 108', 108" to which the horizontal deflectors 106', 106"are connected directly; the vertical deiiectors 107', 107" are connectedacross the signal source 108', 108" through a reversing switch 109 and adelay network 110. This network, shown schematically as composed of apair of ladder-type filter sections, may be a four-terminal network withlumped constants, a coaxial line, or any other combination of circuitelements adapted to impart a progressive phase shift to a rangeoflsignalswithin a predetermined frequency range withoutmateriallyvarying their relative amplitudes.

The beam 111, produced by the electron gun 101-103, impinges upon anoutput electrode generally indicated at 112 and consisting of adielectric backing 113, a layer 114 of resistance material thereon and apair of highly conductive terminal members 11S', 115" in contact withthat layer at diametrically opposite locations. Electrode 112 may besimilar to the target 312 shown in face view in Fig. 3, having itsterminal members 11S', 115 inclined at 45 with respect to the horizontaland vertical planes of deflection; these terminal members are co'nnectedacross an output resistor 116, grounded at its center, and to respectiveoutput terminals 117', 117.`

The operation of the system of Fig. 1 is asfollowss With switch 109 inits right-hand position of, closure, ground on signal terminal 108 isapplied to horizontal deflecting electrode 106 and to verticaldeflecting electrode 107'. It will be convenient to consider these twoelectrodes as located on the negative half-axes of a coordinate system.A positive signal voltage applied to terminal 108" will then appearinstantaneously on electrode 106", thus tending to deflect the beam inthe positive horizontal direction; after a delay 0, dependent upon thesignal frequency, it will also appear on electrode 107" so as to tend todeiiect the beam in the "positive vertical direction. 1f the position ofswitch 109 is now reversed, the phase of the signal on electrode 107" isshifted by 180 and the lagging phase angle 0 isV converted into aleading phase angle of like magnitude. Itwill thus be seen that a phasereversal on one set of deflecting electrodes is equivalent to a transferof delay network from one set of electrodes to the other.

If, for a given signaling frequency, the phase angle 0 is equal to 0,360 or any multiple thereof, the deflected beam will produce a lineartrace bisecting the positive and negative lquadrants of the c-oordinatesystem. In Fig. 2 l have shown a target electrode 212 aligned with suchtrace, comprising an elongated body 214 of resistance material inclinedat 45-to the horizontal and vertical planes of deection. Terminalmembers 215', 215" at the ends of body 214 are connected across seriesresistors 216', 216" which are grounded at their junction, each resistorbeing bridged by a respective condenser 219', 219" serving as a shuntfor impulses due to brief crossings of target 212 by the beam when thelatter is deflected by signal waves not having the proper frequency. Theoutput terminals of the system are shown at 217', 217".

The target electrode 312 of Fig. 3 comprises a rectangular resistivebody 314 bounded on two opposite edges by terminal strips 315', 315",the latter being connected across output terminals 317', 317" which arebridged by resistor 316 grounded at its midpoint. Owing to thearrangement of strips 315', 315", the face of electrode 312 (as also ofelectrode 212) has but two axes of symmetry even if its resistance body314y is a perfect square; these axes are again inclined at angles to thehorizontal and vertical planes of deflection.

If f, is a signal frequency for which the phase delay introduced bynetwork 110 is 180 or an odd multiple thereof, and if f2 is a frequencyfor which this phase delay is zero or any even multiple of 180 asconsidered in connection with Fig. 2, the trace of the beam will be astraight line perpendicular (f1) or parallel (f2) to the Strip`s 315',315". In the lirst instance the output at terminals 317', 317" will be amaximum; in the second instance this output will vanish. When the switch109 is reversed, the positions of traces f1 and f2 will be interchangedwhereby only the latter frequency will produce an output. It will thusbe seen that the device now being described acts as a filter having,r `apass band centered on a first frequency f1 and a stop band centered on asecond frequency f2, the switch 109 serving as a means for interchangingthe positions of these bands in the frequency spectrum.

A frequency f3, for which the phase delay is 90 or an odd multiplethereof, will give rise to -a circular trace as likewise shown in Fig.3; this trace will be unaffected by reversals of switch 109, producingoutput oscillations of equal amplitudes in the two switch positions.Intermediate frequencies will produce elliptical traces having theirmajor axes perpendicular (L) or parallel (f5) to terminal strips 315',315". These frequencies will, accordingly, result in a relatively largeand a relatively small output respectively, subject to reversal byoperation of switch 109. It will be noted that the relative amplitudesof the output oscillations in Fig. 3 are determined by the extent of thebeam sweep in a preferred dimension (perpendicular to strips 315', 315")and are substantially independent of the location of the beam trace onthe face of electrode 312.

In Fig. 4 I have shown a type of target adapted to discriminate betweena single, pure sine wave of predetermined frequency on the one hand andother types of waves, including or not including the desired frequency,on the other. Such devices are particularly useful in voice frequencysignaling systems of telephone circuits wherein it is necessary to guardagainst false operation of a relay or other switching mechanism byspeech waves that happen to contain the critical frequency.

The target of Fig. 4 comprises three concentric ring electrodes ofhighly conductive material, indicated at 412er, 412b and 412Crespectively. Each of these electrodes is connected to a respectiveoutput resistor 416a, 41611, 416C and a respective output terminal417a", 417b", 417e", the later in turn being connected to groundedterminal 417 by way of respective condensers 41911, 41%, and 419C.

If an incoming signal consists of a pure sine wave of frequency f3, thebeam 111 will trace a circular path which, depending upon they amplitudeof the wave, may be made to coincide with one of the electrodes 416a,416b, 416e, thus giving rise to a D.-C. output signal at thecorresponding set of terminals. If the frequency of the wave has a valueother than f, as defined above, the

4 beam will only intermittently intersect the electrodes of Fig. 4,thereby producing a series of short pulses which will be ineffective toresult in any switching operation, being largely shunted to groundthrough the respective condensers 41911, 419b, 419C (the same as in thesystem of Fig. 2). A similar situation will exist if some other signalis superimposed upon the wave of frequency f3, Since then the trace will be displaced from its concentric position with respect to theelectrodes 412a, 412b, 412e.

Fig. 5 shows a single electrode 512 consisting of a conductive stripinclined at 45 `and connected to an output resistor 516, the outputterminals 517', 517" being bridged by a condenser 519. From theforegoing it will be understood that this electrode responds only to asignal wave of frequency f2 and substantially rejects all other waves,but that in contradistinction to the target 212 of Fig. 2 it produces asteady output potential rather than an oscillating voltage in responseto such signal. The output appearing across terminals will, furthermore,be independent of the amplitude of the incoming signal wave.

Fig. 6 illustrates a target combining the features of the systems ofFigs. 2 `and 4, designed to produce any oscillatory output which ischanneled into one of several load circuits according to the amplitudeof the incoming wave. This figure shows three concentric electrodes612a, 612b, 612C comprising respective annular layers 614:1, 614b, 614eof resistance material and pairs of diametrically opposite terminalelements 615g', 615a"; 61512', 615b"; 615e', 615C". Each of theseterminal elements is grounded by way of a respective output resistor616:1', 616b', 616C' and 616a", 616b", 616e", shunted by a respectivecondenser 619a', 619b', 619C' and 619a", 61919", 619C". Thecorresponding output terminals are indicated at 617a', 61711', 617e' and617a", 617/1", 617C".

In Fig. 7 I have shown a target consisting of three concentric annularelectrodes 712g, 7125, 712C, which are similar to the electrodes of Fig.6 but are in the form of elongated ellipses rather than circles. Again,each electrode consists of resistance material and is provided withdiametrically opposite terminal elements 715g', 715a", 715b', 715b";715e', 715e". It will be noted that all of these ellipses are similar,i. e. that the ratio of their axes is the same (corresponding to apredetermined signal frequency, such as f5), and that the major axes areinclined at 45 to the planes of deflection. The output connection of thetarget electrodes have not been shown in Fig. 7 and may be the same lasin Fig. 6. The positioning of the terminal members at the apices of theellipses is convenient but not essential.

The reversing switch 109, which would be functionless in the case ofcircular target electrodes as shown in Figs. 4 and 6, may be used inconjunction with the system of Fig. 7 for varying the frequency to whichthe system iS designed to respond, as by changing it fromf5 to L. Itwill be understood that a steady rather than an oscillating output maybe derived from the electrodes 712a, 71217, 712r.` by constructing themof highly conductive material and connecting them across respective loadresistors in the manner illustrated in Fig. 4.

From the foregoing description it will be apparent that the beam of thecathode ray tube will describe a generally elliptical path in responseto any particular frequency component within the frequency bandconsidered, the straight lines f1, f2 and the circular trace y', beingextreme and specific instances of such elliptical path. Useful outputwill, of course, also be obtainable if only part of the beam traceregisters with the target, as where a portion of one or more of theannular electrodes in Figs. 4, 6 and 7 is omitted. The invention is,accordingly, not limited to the specific embodiments described andillustrated but is capable of different modes of realization withoutdeparting from the spirit and scope of the appended claims.

I claim:

l. A wave filter comprising a source of electrons, focusing meansforming said electrons into a beam, a

source of 'signal waves, first and second deecting means positionedalong the path of Isaid beam, first circuit means connecting said sourceof signal waves to said iirst defleeting means for deecting said beam inone plane under the control of said waves, second circuit meansconnecting said source of signal Waves to said second deliecting meansfor deflecting said beam in another plane under the control `of saidwaves but with a phase delay relative to its deection in said one plane,and target means in the path of said beam comprising at least one outputelectrode having at least one but not more than two axes of symmetryeach inclined with respect to said planes.

2. A wave iilter according to claim 1, further comprising switch meansfor reversing the relative phase of said signal waves as applied to saidfirst and second deflecting means.

3. A wave filter -according to claim l, wherein said output electrode isin the form of an elongated ellipse.

4. A wave lter according to claim 3, wherein said output electrodecomprises a body of resistance material provided with output connectionsat diametrically opposite points.

5. A wave lter -according to claim 1, wherein said output electrodecomprises an elongated strip bisecting the angle between said planes.

6. A wave lter according to claim l, wherein said output electrodecomprises a substantially rectangular element of resistance materialprovided with highly conductive terminal strips along opposite edges,said terminal strips extending substantially parallel to the bisector ofthe angle between said planes.

7. In a cathode ray tube, in combination, means for producing anelectron beam, a source of signal waves, means connected to said sourcefor deiiecting said beam along generally elliptical traces in responseto signal waves of a predetermined frequency, a plurality of similar,concentric annular output electrodes shaped and positioned to coincidewith said traces for different amplitudes of said waves of predeterminedfrequency, and a load circuit connected to each of said outputelectrodes.

8. The combination according to claim 7, wherein said output electrodesare in the shape of elongated ellipses.

9. The combination according t'o claim 7, wherein said output electrodescomprise annular bodies of resistance material provided with outputconnections at diametrically opposite points.

10. In a cathode ray tube a target electrode having the shape of atleast a substantial part of an elongated ellipse.

11. In a cathode ray tube a target electrode comprising an elongatedelliptical body of resistance material and output connections atdiametrically opposite points of said body.

12. In a cathode ray tube, in combination, means for producing anelectron beam, a source of signal waves, rst means connected to saidsource for deecting said beam in one plane in the rhythm of said Waves,second means connected to said source for deiiecting said beam inanother plane in the rhythm of said waves but out of phase with thedeflection of said beam in said one plane, and an elliptical targetelectrode in the path of 'said beam, said electrode having a major axisinclined with respect to said planes.

13. The combination `according to claim 12, wherein said planes areperpendicular to each other, said major axis extending at with respectto said planes.

14. The combination Iaccording to claim 12, further including switchmeans for reversing the relative phase of deection of said beam in saidplanes.

References Cited in the le of this patent UNITED STATES PATENTS

